If $x \diamond y = 2x-6$ and $x \boxdot y = 4x-2y$, find $-2 \boxdot (-6 \diamond 5)$.
Solution: First, find $-6 \diamond 5$ $ -6 \diamond 5 = (2)(-6)-6$ $ \hphantom{-6 \diamond 5} = -18$ Now, find $-2 \boxdot -18$ $ -2 \boxdot -18 = (4)(-2)-(2)(-18)$ $ \hphantom{-2 \boxdot -18} = 28$.